/****************************************************************************
 * crypto/poly1305.c
 * $OpenBSD: poly1305.c,v 1.2 2020/07/22 13:54:30 tobhe Exp $
 *
 * Public Domain poly1305 from Andrew Moon
 * Based on poly1305-donna.c, poly1305-donna-32.h and poly1305-donna.h from:
 *   https://github.com/floodyberry/poly1305-donna
 ****************************************************************************/

/****************************************************************************
 * Included Files
 ****************************************************************************/

#include <sys/types.h>

#include <crypto/poly1305.h>

/* poly1305 implementation using 32 bit * 32 bit = 64 bit multiplication
 * and 64 bit addition.
 */

/* interpret four 8 bit unsigned integers as a
 * 32 bit unsigned integer in little endian
 */

static unsigned long U8TO32(FAR const unsigned char *p)
{
  return (((unsigned long)(p[0] & 0xff)) |
      ((unsigned long)(p[1] & 0xff) <<  8) |
      ((unsigned long)(p[2] & 0xff) << 16) |
      ((unsigned long)(p[3] & 0xff) << 24));
}

/* store a 32 bit unsigned integer as four
 * 8 bit unsigned integers in little endian
 */

static void U32TO8(FAR unsigned char *p, unsigned long v)
{
  p[0] = (v) & 0xff;
  p[1] = (v >>  8) & 0xff;
  p[2] = (v >> 16) & 0xff;
  p[3] = (v >> 24) & 0xff;
}

/****************************************************************************
 * Public Functions
 ****************************************************************************/

void poly1305_begin(FAR poly1305_state *st, FAR const unsigned char *key)
{
  /* r &= 0xffffffc0ffffffc0ffffffc0fffffff */

  st->r[0] = (U8TO32(&key[0])) & 0x3ffffff;
  st->r[1] = (U8TO32(&key[3]) >> 2) & 0x3ffff03;
  st->r[2] = (U8TO32(&key[6]) >> 4) & 0x3ffc0ff;
  st->r[3] = (U8TO32(&key[9]) >> 6) & 0x3f03fff;
  st->r[4] = (U8TO32(&key[12]) >> 8) & 0x00fffff;

  /* h = 0 */

  st->h[0] = 0;
  st->h[1] = 0;
  st->h[2] = 0;
  st->h[3] = 0;
  st->h[4] = 0;

  /* save pad for later */

  st->pad[0] = U8TO32(&key[16]);
  st->pad[1] = U8TO32(&key[20]);
  st->pad[2] = U8TO32(&key[24]);
  st->pad[3] = U8TO32(&key[28]);

  st->leftover = 0;
  st->final = 0;
}

static void poly1305_blocks(FAR poly1305_state *st,
                            FAR const unsigned char *m,
                            size_t bytes)
{
  const unsigned long hibit = (st->final) ? 0 : (1 << 24); /* 1 << 128 */
  unsigned long r0;
  unsigned long r1;
  unsigned long r2;
  unsigned long r3;
  unsigned long r4;
  unsigned long s1;
  unsigned long s2;
  unsigned long s3;
  unsigned long s4;
  unsigned long h0;
  unsigned long h1;
  unsigned long h2;
  unsigned long h3;
  unsigned long h4;
  unsigned long long d0;
  unsigned long long d1;
  unsigned long long d2;
  unsigned long long d3;
  unsigned long long d4;
  unsigned long c;

  r0 = st->r[0];
  r1 = st->r[1];
  r2 = st->r[2];
  r3 = st->r[3];
  r4 = st->r[4];

  s1 = r1 * 5;
  s2 = r2 * 5;
  s3 = r3 * 5;
  s4 = r4 * 5;

  h0 = st->h[0];
  h1 = st->h[1];
  h2 = st->h[2];
  h3 = st->h[3];
  h4 = st->h[4];

  while (bytes >= poly1305_block_size)
    {
      /* h += m[i] */

      h0 += (U8TO32(m + 0)) & 0x3ffffff;
      h1 += (U8TO32(m + 3) >> 2) & 0x3ffffff;
      h2 += (U8TO32(m + 6) >> 4) & 0x3ffffff;
      h3 += (U8TO32(m + 9) >> 6) & 0x3ffffff;
      h4 += (U8TO32(m + 12) >> 8) | hibit;

      /* h *= r */

      d0 = ((unsigned long long)h0 * r0) +
          ((unsigned long long)h1 * s4) +
          ((unsigned long long)h2 * s3) +
          ((unsigned long long)h3 * s2) +
          ((unsigned long long)h4 * s1);
      d1 = ((unsigned long long)h0 * r1) +
          ((unsigned long long)h1 * r0) +
          ((unsigned long long)h2 * s4) +
          ((unsigned long long)h3 * s3) +
          ((unsigned long long)h4 * s2);
      d2 = ((unsigned long long)h0 * r2) +
          ((unsigned long long)h1 * r1) +
          ((unsigned long long)h2 * r0) +
          ((unsigned long long)h3 * s4) +
          ((unsigned long long)h4 * s3);
      d3 = ((unsigned long long)h0 * r3) +
          ((unsigned long long)h1 * r2) +
          ((unsigned long long)h2 * r1) +
          ((unsigned long long)h3 * r0) +
          ((unsigned long long)h4 * s4);
      d4 = ((unsigned long long)h0 * r4) +
          ((unsigned long long)h1 * r3) +
          ((unsigned long long)h2 * r2) +
          ((unsigned long long)h3 * r1) +
          ((unsigned long long)h4 * r0);

      /* (partial) h %= p */

      c = (unsigned long)(d0 >> 26);
      h0 = (unsigned long)d0 & 0x3ffffff;
      d1 += c;
      c = (unsigned long)(d1 >> 26);
      h1 = (unsigned long)d1 & 0x3ffffff;
      d2 += c;
      c = (unsigned long)(d2 >> 26);
      h2 = (unsigned long)d2 & 0x3ffffff;
      d3 += c;
      c = (unsigned long)(d3 >> 26);
      h3 = (unsigned long)d3 & 0x3ffffff;
      d4 += c;
      c = (unsigned long)(d4 >> 26);
      h4 = (unsigned long)d4 & 0x3ffffff;
      h0 += c * 5;
      c = (h0 >> 26);
      h0 = h0 & 0x3ffffff;
      h1 += c;

      m += poly1305_block_size;
      bytes -= poly1305_block_size;
    }

  st->h[0] = h0;
  st->h[1] = h1;
  st->h[2] = h2;
  st->h[3] = h3;
  st->h[4] = h4;
}

void poly1305_update(FAR poly1305_state *st,
                     FAR const unsigned char *m,
                     size_t bytes)
{
  size_t i;

  /* handle leftover */

  if (st->leftover)
    {
      size_t want = (poly1305_block_size - st->leftover);
      if (want > bytes)
        {
          want = bytes;
        }

      for (i = 0; i < want; i++)
        {
          st->buffer[st->leftover + i] = m[i];
        }

      bytes -= want;
      m += want;
      st->leftover += want;
      if (st->leftover < poly1305_block_size)
        {
          return;
        }

      poly1305_blocks(st, st->buffer, poly1305_block_size);
      st->leftover = 0;
    }

  /* process full blocks */

  if (bytes >= poly1305_block_size)
    {
      size_t want = (bytes & ~(poly1305_block_size - 1));
      poly1305_blocks(st, m, want);
      m += want;
      bytes -= want;
    }

  /* store leftover */

  if (bytes)
    {
      for (i = 0; i < bytes; i++)
        {
          st->buffer[st->leftover + i] = m[i];
        }

      st->leftover += bytes;
    }
}

void poly1305_finish(FAR poly1305_state *st, FAR unsigned char *mac)
{
  unsigned long h0;
  unsigned long h1;
  unsigned long h2;
  unsigned long h3;
  unsigned long h4;
  unsigned long c;
  unsigned long g0;
  unsigned long g1;
  unsigned long g2;
  unsigned long g3;
  unsigned long g4;
  unsigned long long f;
  unsigned long mask;

  /* process the remaining block */

  if (st->leftover)
    {
      size_t i = st->leftover;
      st->buffer[i++] = 1;
      for (; i < poly1305_block_size; i++)
        st->buffer[i] = 0;
      st->final = 1;
      poly1305_blocks(st, st->buffer, poly1305_block_size);
    }

  /* fully carry h */

  h0 = st->h[0];
  h1 = st->h[1];
  h2 = st->h[2];
  h3 = st->h[3];
  h4 = st->h[4];

  c = h1 >> 26;
  h1 = h1 & 0x3ffffff;
  h2 += c;
  c = h2 >> 26;
  h2 = h2 & 0x3ffffff;
  h3 += c;
  c = h3 >> 26;
  h3 = h3 & 0x3ffffff;
  h4 += c;
  c = h4 >> 26;
  h4 = h4 & 0x3ffffff;
  h0 += c * 5;
  c = h0 >> 26;
  h0 = h0 & 0x3ffffff;
  h1 += c;

  /* compute h + -p */

  g0 = h0 + 5;
  c = g0 >> 26;
  g0 &= 0x3ffffff;
  g1 = h1 + c;
  c = g1 >> 26;
  g1 &= 0x3ffffff;
  g2 = h2 + c;
  c = g2 >> 26;
  g2 &= 0x3ffffff;
  g3 = h3 + c;
  c = g3 >> 26;
  g3 &= 0x3ffffff;
  g4 = h4 + c - (1 << 26);

  /* select h if h < p, or h + -p if h >= p */

  mask = (g4 >> ((sizeof(unsigned long) * 8) - 1)) - 1;
  g0 &= mask;
  g1 &= mask;
  g2 &= mask;
  g3 &= mask;
  g4 &= mask;
  mask = ~mask;
  h0 = (h0 & mask) | g0;
  h1 = (h1 & mask) | g1;
  h2 = (h2 & mask) | g2;
  h3 = (h3 & mask) | g3;
  h4 = (h4 & mask) | g4;

  /* h = h % (2^128) */

  h0 = ((h0) | (h1 << 26)) & 0xffffffff;
  h1 = ((h1 >>  6) | (h2 << 20)) & 0xffffffff;
  h2 = ((h2 >> 12) | (h3 << 14)) & 0xffffffff;
  h3 = ((h3 >> 18) | (h4 <<  8)) & 0xffffffff;

  /* mac = (h + pad) % (2^128) */

  f = (unsigned long long)h0 + st->pad[0];
  h0 = (unsigned long)f;
  f = (unsigned long long)h1 + st->pad[1] + (f >> 32);
  h1 = (unsigned long)f;
  f = (unsigned long long)h2 + st->pad[2] + (f >> 32);
  h2 = (unsigned long)f;
  f = (unsigned long long)h3 + st->pad[3] + (f >> 32);
  h3 = (unsigned long)f;

  U32TO8(mac + 0, h0);
  U32TO8(mac + 4, h1);
  U32TO8(mac + 8, h2);
  U32TO8(mac + 12, h3);

  /* zero out the state */

  st->h[0] = 0;
  st->h[1] = 0;
  st->h[2] = 0;
  st->h[3] = 0;
  st->h[4] = 0;
  st->r[0] = 0;
  st->r[1] = 0;
  st->r[2] = 0;
  st->r[3] = 0;
  st->r[4] = 0;
  st->pad[0] = 0;
  st->pad[1] = 0;
  st->pad[2] = 0;
  st->pad[3] = 0;
}
